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Light scattering and absorption in tissue - models and measurements

Enejder, Annika M K LU (1997)
Abstract (Swedish)
Popular Abstract in Swedish

Ljusspridning och absorption i biologisk vävnad - modeller och mätningar



Visionerna är stora i medicingruppen på avdelningen för atomfysik, LTH, nämligen att utveckla nya metoder för förfinad diagnostik och selektiv behandling av cancer, hjärt- och kärlsjukdomar med hjälp av laserljus.



Möjligheten till att med ljus detektera och karakterisera sjuk vävnad, exempelvis tumörvävnad, fibrös hjärtmuskelvävnad, kärlvävnad med inlagringar av kalcium etc., baseras på att den sprider och absorberar ljus på ett sätt som skiljer sig från det i den friska vävnaden. Det kan dels bero på inlagringar och förändringar av karakteristiska molekyler, men även på förändringar i... (More)
Popular Abstract in Swedish

Ljusspridning och absorption i biologisk vävnad - modeller och mätningar



Visionerna är stora i medicingruppen på avdelningen för atomfysik, LTH, nämligen att utveckla nya metoder för förfinad diagnostik och selektiv behandling av cancer, hjärt- och kärlsjukdomar med hjälp av laserljus.



Möjligheten till att med ljus detektera och karakterisera sjuk vävnad, exempelvis tumörvävnad, fibrös hjärtmuskelvävnad, kärlvävnad med inlagringar av kalcium etc., baseras på att den sprider och absorberar ljus på ett sätt som skiljer sig från det i den friska vävnaden. Det kan dels bero på inlagringar och förändringar av karakteristiska molekyler, men även på förändringar i form och antal av hela celler och deras organeller. Mitt arbete har bestått i att försöka förstå hur dessa vävnadens mikroskopiska egenskaper påverkar spridnings- och absorptionsegenskaperna både genom teoretiska beräkningar och genom experimentella studier av tillbakareflekterat och transmitterat elastiskt spritt ljus, liksom fluorescens ljus, från vävnad - speciellt blod. Jag har exempelvis visat att ju mer utsträckt form celler har, desto mer asymmetrisk karaktär har den rumsliga fördelningen av det spridda ljuset. Vidare har jag demonstrerat att lutningen av en uppmätt reflektans- och transmittanskurva som funktion av våglängden kan i princip användas för att uppskatta storleksordningen på den komponent i vävnaden (cell, cellmembran, organell, biomolekylkomplex etc.) som orsakar den huvudsakliga delen av ljusspridningen. Detta öppnar upp dörren för att på ett enkelt sätt få ut information om den mikroskopiska strukturen i vävnad, intressant ur ett optiskt perspektiv.



Behandling med hjälp av laserljus bygger i princip på att ljusets energi förs över till vävnadens biomolekyler, eller till utifrån tillförda s.k. fotosensibiliserare, och orsakar antingen en temperaturhöjning eller en kemisk reaktion. Dessa processer förstör i sin tur den kringliggande maligna vävnaden. För en effektiv behandling är det viktigt att hela det maligna området behandlas, vilket till stor utsträckning bestäms av fördelningen av behandlingsljuset i vävnaden. Denna ljusfördelning bestäms i sin tur av vävnadens spridnings- och absorptionsegenskaper. Jag har mätt upp dessa egenskaper på muskel och levervävnad och visat att de ändras under både behandlingar baserade på värme och på fotokemiska reaktioner. För korrekt dosimetri av behandlingsljuset är det viktigt att ta med denna ändring av vävnadens optiska egenskaper i beräkningarna.



Det centrala i denna avhandling är alltså studier av de optiska spridnings- och absorptionsegenskaperna, d.v.s de optiska storheterna för biologisk vävnad, i anknytning till laserdiagnostik- och behandlingsmetoder. (Less)
Abstract
In this work a number of theoretical models, describing light propagation in matter, have been applied to and developed for the examination of tissue. The aim was to model the light scattering and absorption in tissue in order to improve the understanding of underlying mechanisms of laser-based diagnostics and treatment modalities utilised for cancer and cardiovascular diseases. The models studied ranged from the simplest Beer-Lambert law, assuming a plain exponential behaviour of the light transport, to solutions of Maxwell's fundamental equations for the scattering of electromagnetic waves. The latter approach was specifically used for computations of light scattering by red blood cell volume-equivalent spheroids by applying the... (More)
In this work a number of theoretical models, describing light propagation in matter, have been applied to and developed for the examination of tissue. The aim was to model the light scattering and absorption in tissue in order to improve the understanding of underlying mechanisms of laser-based diagnostics and treatment modalities utilised for cancer and cardiovascular diseases. The models studied ranged from the simplest Beer-Lambert law, assuming a plain exponential behaviour of the light transport, to solutions of Maxwell's fundamental equations for the scattering of electromagnetic waves. The latter approach was specifically used for computations of light scattering by red blood cell volume-equivalent spheroids by applying the numerical T-matrix formalism. Furthermore, the adding-doubling method, based on the radiative transport equation for multiple scattering, as well as the stochastic Monte Carlo approach, describing the light transport as a random walk process of photons, were employed to model light propagation in dense tissue. The advantages and disadvantages of each model are discussed by exemplifying which applications they are useful for and valid in.



Light scattering and absorption in tissue were also studied in practice. The absorption and scattering characteristics governing the macroscopic light propagation were determined in vitro in terms of the absorption and scattering coefficients as well as the g-factor, employing different integrating-sphere techniques. Changes in these fundamental optical properties were monitored for tissue being exposed to laser-based treatment modalities, such as photodynamic therapy (PDT) and continuous or pulsed thermotherapy. The observed influence on the scattering properties and the manifest increase in the absorption coefficient could be related to mainly morphological and biochemical changes in the blood and/or microvascular damage in the tissue. The latter was further confirmed by an imaging technique showing changes in laser-Doppler signals from moving red blood cells in conjunction with PDT, indicating a local increase in tissue perfusion.



Differences in tissue characteristics were monitored in vivo, in order to distinguish diseased from healthy tissue alone, or in combination with photosensitive agents, employing laser-induced fluorescence (LIF) or near infrared (NIR) spectroscopy. Malignancies in the skin and in the oesophagus could be identified utilising the tumour selective agents ALA and Photofrin respectively, in conjunction with LIF. It was also shown to be possible to spectroscopically distinguish fibrous and fatty heart tissue from healthy myocardium in vitro using either LIF or NIR spectroscopy, if combined with a powerful analysis method such as Principal Component Analysis (PCA). (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Svaasand, Lars O., Norwegian University of Science and Technology, Trondheim, Norway
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Tissue optical properties, Light absorption, Fluorescence spectroscopy, Atomic and molecular physics, NIR spectroscopy, Fysicumarkivet A:1997:Enejder, Light scattering, Atom- och molekylärfysik
pages
279 pages
publisher
Department of Physics, Lund University
defense location
Lecture hall B, Department of Physics, Sölvegatan 14, Lund, Sweden
defense date
1997-10-27 13:15
external identifiers
  • other:ISRN: LUTFD2/(TFAF-1035)/1-119/(1997)
ISBN
91-628-2670-0
language
English
LU publication?
yes
id
d003ad8d-9fc3-447b-9b7c-c80b3bf51fb4 (old id 29645)
date added to LUP
2007-06-14 09:35:11
date last changed
2016-09-19 08:45:06
@phdthesis{d003ad8d-9fc3-447b-9b7c-c80b3bf51fb4,
  abstract     = {In this work a number of theoretical models, describing light propagation in matter, have been applied to and developed for the examination of tissue. The aim was to model the light scattering and absorption in tissue in order to improve the understanding of underlying mechanisms of laser-based diagnostics and treatment modalities utilised for cancer and cardiovascular diseases. The models studied ranged from the simplest Beer-Lambert law, assuming a plain exponential behaviour of the light transport, to solutions of Maxwell's fundamental equations for the scattering of electromagnetic waves. The latter approach was specifically used for computations of light scattering by red blood cell volume-equivalent spheroids by applying the numerical T-matrix formalism. Furthermore, the adding-doubling method, based on the radiative transport equation for multiple scattering, as well as the stochastic Monte Carlo approach, describing the light transport as a random walk process of photons, were employed to model light propagation in dense tissue. The advantages and disadvantages of each model are discussed by exemplifying which applications they are useful for and valid in.<br/><br>
<br/><br>
Light scattering and absorption in tissue were also studied in practice. The absorption and scattering characteristics governing the macroscopic light propagation were determined in vitro in terms of the absorption and scattering coefficients as well as the g-factor, employing different integrating-sphere techniques. Changes in these fundamental optical properties were monitored for tissue being exposed to laser-based treatment modalities, such as photodynamic therapy (PDT) and continuous or pulsed thermotherapy. The observed influence on the scattering properties and the manifest increase in the absorption coefficient could be related to mainly morphological and biochemical changes in the blood and/or microvascular damage in the tissue. The latter was further confirmed by an imaging technique showing changes in laser-Doppler signals from moving red blood cells in conjunction with PDT, indicating a local increase in tissue perfusion.<br/><br>
<br/><br>
Differences in tissue characteristics were monitored in vivo, in order to distinguish diseased from healthy tissue alone, or in combination with photosensitive agents, employing laser-induced fluorescence (LIF) or near infrared (NIR) spectroscopy. Malignancies in the skin and in the oesophagus could be identified utilising the tumour selective agents ALA and Photofrin respectively, in conjunction with LIF. It was also shown to be possible to spectroscopically distinguish fibrous and fatty heart tissue from healthy myocardium in vitro using either LIF or NIR spectroscopy, if combined with a powerful analysis method such as Principal Component Analysis (PCA).},
  author       = {Enejder, Annika M K},
  isbn         = {91-628-2670-0},
  keyword      = {Tissue optical properties,Light absorption,Fluorescence spectroscopy,Atomic and molecular physics,NIR spectroscopy,Fysicumarkivet A:1997:Enejder,Light scattering,Atom- och molekylärfysik},
  language     = {eng},
  pages        = {279},
  publisher    = {Department of Physics, Lund University},
  school       = {Lund University},
  title        = {Light scattering and absorption in tissue - models and measurements},
  year         = {1997},
}